Embodiments of the invention relate generally to diagnostic imaging and, more particularly, to a method and apparatus using low resolution imaging arrays in an imaging application.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotating about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
With recent advances in CT clinical applications, it is desirable to cover an entire organ in a single gantry rotation and in a single projection, so that an entire cardiac acquisition can be completed in a single cardiac cycle. A heart can typically be covered in a cylindrical shaped region with a diameter of 25 cm (in an x-y plane) and a length of 12 cm (in a slice or z-direction) for most patients. In neural perfusion studies it is desirable to cover at least 12 cm along the patient long axis (in z-direction) while continuously scanning the patient during contrast uptake and washout. There are CT scanners on the market that cover, for example, 16 cm along the z-axis and 50 cm field-of-view (FOV) across the patient (in an x-y plane), which are well in excess of that necessary to provide imaging information for cardiac and neural perfusion studies. Thus, for cardiac and neural perfusion studies the region-of-interest (ROI) in the x-y plane is significantly smaller than the full detector coverage of 50 cm.
Scanning a typical organ (i.e., heart or brain) with a 50 cm FOV often provides little additional relevant imaging information, thus a 35 cm FOV is typically adequate for many organ imaging applications. Thus, from a design and cost point of view, it is desirable to reduce the coverage to a FOV (in x-y plane) that is slightly larger than the object-of-interests that are being imaged. For CT reconstruction, however, information outside the ROI may be necessary to faithfully reconstruct an object-of-interest within even a limited FOV. Without this information, typical truncation artifacts may result. Although recent attempts have been made to reconstruct images based on truncated projections, these reconstruction techniques typically result in unstable solutions or require specific knowledge inside the reconstruction FOV. When imaging an object or patient in a larger FOV, relevant imaging information may be, in fact, provided over the entire FOV (50 cm in the above example). Thus, some imaging applications provide adequate imaging data over a 35 cm FOV by using limited additional information outside the FOV to avoid truncation errors, while other imaging applications benefit from obtaining relevant imaging data over the entire 50 cm FOV. In both cases (limited FOV and full FOV), it is desirable to obtain imaging data using a detector having a full 50 cm FOV. The cost of such a scanner can be prohibitive, however.
Therefore, it would be desirable to design an apparatus and method to reduce cost of a CT system, while providing full and limited FOV imaging capability.